Safe birdhouse designs omit perches entirely. Birds don’t need them—they’re perfectly capable of clinging to the entrance hole. Smooth, perch-free designs are safer, cleaner, and more supportive of native species.
House sparrows: Highly aggressive, they often kill or evict native birds from nest boxes. A perch gives them a convenient staging spot to dominate the entrance.
Starlings: Larger and more forceful, starlings can use perches to gain leverage when attacking or claiming a box.
Impact on natives: Bluebirds, chickadees, wrens, and other cavity-nesters are less aggressive. When invasive species gain easy access, they’re quickly displaced, reducing native populations.
To support native birds, experts recommend perch-free designs combined with entrance-hole sizes tailored to the species you want to attract. This way, invasive species are less likely to fit or settle in.